Phonemic Awareness (PA) is:

the ability to hear and manipulate the sounds in spoken words and the understanding that spoken words and syllables are made up of sequences of speech sounds (Yopp, 1992; see References).

essential to learning to read in an alphabetic writing system, because letters represent sounds or phonemes. Without phonemic awareness, phonics makes little sense.

fundamental to mapping speech to print. If a child cannot hear that "man" and "moon" begin with the same sound or cannot blend the sounds
/rrrrrruuuuuunnnnn/ into the word "run", he or she may have great difficulty connecting sounds with their written symbols or blending sounds to make a word.

essential to learning to read in an alphabetic writing system.

a strong predictor of children who experience early reading success.

An important distinction:

Phonemic awareness is NOT phonics.

Phonemic awareness is AUDITORY and does not involve words in print.

Phonemic Awareness is important ...

It requires readers to notice how letters represent sounds. It primes readers for print.

It gives readers a way to approach sounding out and reading new words.

It helps readers understand the alphabetic principle (that the letters in words are systematically represented by sounds).

...but difficult:

Although there are 26 letters in the English language, there are approximately 40 phonemes, or sound units, in the English language. (NOTE: the number of phonemes varies across sources.)

Sounds are represented in 250 different spellings (e.g., /f/ as in ph, f, gh, ff).

The sound units (phonemes) are not inherently obvious and must be taught. The sounds that make up words are "coarticulated;" that is, they are not distinctly separate from each other.

Definitions of key PA terminology:

Phoneme: A phoneme is a speech sound. It is the smallest unit of language and has no inherent meaning.

Phonemic Awareness: The ability to hear and manipulate the sounds in spoken words, and the understanding that spoken words and syllables are made up of sequences of speech sounds (Yopp, 1992; see References). Phonemic awareness involves hearing language at the phoneme level.

Phonics: use of the code (sound-symbol relationships to recognize words.

Phonological Awareness: The ability to hear and manipulate the sound structure of language. This is an encompassing term that involves working with the sounds of language at the word, syllable, and phoneme level.

Phonemic Awareness Research Says:

"The best predictor of reading difficulty in kindergarten or first grade is the inability to segment words and syllables into constituent sound units (phonemic awareness)" (Lyon, 1995; see References).

The ability to hear and manipulate phonemes plays a causal role in the acquisition of beginning reading skills (Smith, Simmons, & Kame'enui, 1998; see References).

There is considerable evidence that the primary difference between good and poor readers lies in the good reader's phonological processing ability.

The effects of training phonological awareness and learning to read are mutually supportive. "Reading and phonemic awareness are mutually reinforcing: Phonemic awareness is necessary for reading, and reading, in turn, improves phonemic awareness still further." (Shaywitz, 2003, see References)